Orthopedic surgery can require bone drilling for the repair of fractures or insertion of implants or other devices. The resulting holes can be used to accept screws, implants and other devices to exert pressure, fixation or reduction of the bone or to place prosthetic joints or other implants. Other medical procedures can require access to bone. For example, the interosseous canal of bone can be accessed to allow fluid administration. Bone can also be accessed to allow the harvesting of bone, collection of bone marrow cores, or for the aspiration of bone marrow for diagnostic or therapeutic purposes. During any procedure where a drill or other driver is used to advance a tool into and through bone, the user must consciously and carefully limit the penetration to the desired depth. If the user allows the tool to penetrate further, the patient can suffer injury to distal structures such as nerve, brain, spinal cord, artery, vein, muscle, fascia, bone or joint space structures. These types of injuries can lead to severe patient morbidity and even death. The devices inserted to a drilled bore often must fit within a narrow length range that can vary sometimes by no more than a millimeter or less.
Once the drilling of a bone is safely complete, it is often prudent to obtain the depth of the bore made by the drilling tool. Many procedures require knowledge of the depth of tool penetration, such as in the placement of internal fixation devices, screws and other implantable hardware. Selecting an appropriate length of the screw or other implant necessary for the procedure depends upon such knowledge of the bore's depth. Conventional techniques used in the art are often inconvenient, time consuming and unreliable often requiring trial and error and multiple exposures to radiographs before the proper implant insertion is achieved.
A common way to obtain the depth of the bore formed by a drilling tool is to use a depth gauge. Often users must interrupt the drilling procedure in order to palpate or measure with a depth gauge whether or not the desired depth has been achieved. In many instances a user will take a radiograph during a drilling procedure to confirm the appropriate depth of penetration has been achieved or take a radiograph while the depth gauge is in place to ensure the information the gauge provides is accurate. Depth gauges used in the art can be inaccurate resulting in a user placing a screw of an inappropriate length not often identified until a confirming radiograph is taken. Each radiograph taken increases the radiation exposure of the surgeon, staff and patient in the operating suite. Depth gauges known in the art can also break and require the user to retrieve it from the bore. Inconvenient and inaccurate depth measurement devices and methods can result in improperly sized screws that must be removed and replaced with new properly sized screws. Wasted hardware, increased disruptions and delays in orthopedic procedures ultimately increase the expense of a procedure as well as expose the surgeon, staff and the patient to unnecessary radiation. The cost of the additional time, the wasted hardware and the radiation exposure are quite significant.